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The advantage seems to be that you would not have to unscrew and re-screw the valve cap every time you want to double check the tire pressure.

What is everyone's opinion about how often you need to double check your tire pressures with the pressure monitoring system that comes on a 2008 335?

The Measurement Ltd. MS-4359 is a unique programmable tire pressure monitoring system. Built in tire pressure monitoring systems can cost 100's of dollars and require professional installation. The MS-4359 is a practical and economical alternative. The system features smart valve caps, which will remember your factory recommended pressure setting. Simply program the factory recommended tire pressure setting into the caps with the easy to use programmer/gauge, touch the programmer/gauge to the cap and it automatically checks the pressure with an accuracy of within 1 PSI. The gauge then gives you a reading using the familiar stop light indicator: green = ok, yellow = getting low, or red = needs air. Check the pressure in all four tires in less than a minute! The programmer/gauge also acts as a standard tire gauge with accuracy from 5-99 PSI in .5 PSI increments so when you do need to add air to your tires, you can insure an accurate fill. Correct tire pressure can increase the life of your tires and improve your gas mileage ¿ maintain that correct tire pressure easily with the MS-4359 Tire Pressure Monitoring System.